The overall objective of this study is to investigate the incidence, severity and etiology of chronobiological dysfunction in the blind, and develop a rational approach to therapy. We plan to follow up our previous survey of the blind community with a detailed questionnaire modified so that the questions are specifically addressed to the blind. These questions will be aimed at investigating the incidence and nature of sleep/wake complaints and biological rhythm dysfunction. This investigation will be aided by cooperation of Dr. Joan Chase of Rutgers Medical School who has studied and is following up about 200 young people with retrolental fibroplasia. Selected blind subjects will undergo ambulatory monitoring using a unique Portable Temperature/Activity Recording Device. Other blind subjects will undergo a special inpatient 48 hour Rest/Activity continuous blood-withdrawal study with special attention to changes in plasma melatonin. The final clinical study involves use of a recently constructed time-isolation facility, controlled by STIFM, a microprocessor-based monitor. We also plan to develop effective methods of treatment for chronobiological dysfunction.